Neil Macdonald wrote an interesting and very accessible piece today about US right-to-work laws, specifically considering Michigan's incoming law.
Right to work laws basically remove any requirement for workers who benefit from union contracts to pay dues or be members. They also remove the obligation of unionized employers to deduct dues from worker paycheques.
In effect, these laws undermine the financial security of the union. Unions are forced to spend resources chasing dues and representing free-riders, rather than seeking improved working conditions or political change beneficial to workers. Which is, of course, the point of "right-to-work" laws.
Combining right-to-work laws with the US preference for the employment-at-will doctrine and a loose labour market and you have a recipe for low-wage work.
-- Bob Barnetson